1. Field of the Invention
Example embodiments generally relate to time-temperature indicator devices and, more particularly, relate to a long-life and unpowered, time-temperature indicator.
2. Description of the Related Art
Many perishable products have a limited lifetime that can be at least in part dependent upon the temperatures to which the products are exposed. Moreover, in some cases, the length time of such exposure may further impact the rate of degradation of the product. For example, some foods and pharmaceuticals may have a nominal expiration date at a certain temperature, but may expire more quickly if they are exposed to other temperatures for at least a given time period.
Since products are often shipped and may change hands and experience different conditions during their shipment process, it cannot be assumed that a product that was shipped at a particular temperature, and arrives at the same temperature, has been maintained at that temperature throughout the shipping process. Moreover, the simple fact that a temperature fluctuation was encountered, even a fluctuation above a certain amount, may not necessarily mean that the product is compromised. Thus, an indication that a certain temperature was reached [for which there are existing commercial devices], without a corresponding indication of the amount of time that the exposure to that temperature lasted may lead to unnecessary destruction of products.
To address the issues described above, time-temperature indicators of various types have been developed. However, many such time-temperature indicators rely on powered monitoring devices, chemical reactions or diffusion of controlled dyes. However, properties of the chemicals or dyes may change over time, and the power is only available for a limited time. Thus, the life time of such devices may be limited, and such devices may not be very robust.